During this period, test tubes were occasionally mixed. After the prescribed time, 2 mL of n-hexane and deionized water was added to tubes, followed by vortexing at 500×g for 3 min. The layers were allowed to separate for 30 min, then the supernatant was transferred to GC vials and injected into a GC with a methyl lignoserate-coated polar capillary column
(filmthickness 0.25 m) (SP-2330; Supelco, Bellefonte, PA, USA) (100-m×0.32-mm) and FID (15).